Comparative study of the effect of 1,25 dihydroxyvitamin D3 and 24,25-dihydroxyvitamin D3 on calcium homeostasis and bone tissue state in rats during hypokinesia

Abstract: Preventive administration of vitamin D3 active metabolites 1.25(OH)2D3 and 24.25(OH)2D3 into growing rats, kept under conditions of long-term hard hypokinesia, normalized Ca metabolism and the state of bone tissue depending on the preparations dose and their combination. 1.25(OH)2D3 at a dose of 0.03 microgram per an animal daily augmented effectively the Ca absorption in small intestine, corrected hypocalcemia, increased slightly the bone tissue density and the Ca and P content in the tissue as well as it elevated the volume of spongiosa, width of the epiphysial growth plate (EGP) and the amount of osteoclasts. After an increase of the metabolite dose up to 0.15 microgram hypercalcemia, hyperphosphatemia, intensive resorption of bone tissue, distinct increase in the osteoclasts content and ectopic calcification were observed. Administration of 1.35(OH)2D3 and 24.25(OH)2D3 combination (0.03 microgram and 0.25 or 1.25 micrograms, respectively) or only 24.25(OH)2D3 at a dose of 1.25 micrograms caused a restoration of Ca absorption in intestine and of its level in blood as well as mineral composition, density of bone tissue, volume of primary and secondary spongiosa were normalized, while the EGP width and amount of osteoclasts remained decreased. Synergic effect of 1.25(OH)2D3 and 24.25(OH)2D3 in rats appears to depend on their various functions in regulation of Ca metabolism, in development and remodelation of bone tissue, thus indicating that these metabolites of vitamin D3 should be used simultaneously under conditions of hypokinesia for prophylactic purposes.